The mechanical properties of dentin are important for understanding how masticatory strains are distributed throughout a tooth, and for predicting how stresses and strains are altered due to restoration procedures, age, and disease. In particular, knowledge of the mechanical properties is a first step towards predicting the behavior of the dentin/restoration interface, and how aging and disease processes alter the strength of dentin. The purpose of this project is to determine the hardness, elastic modulus, and shear properties of dentin as a function of location, age, and gender. Unlike earlier work, which established many of these properties on a macroscopic, or continuum, scale that averaged over wide variations in dentin morphology, this work will quantify the mechanical properties of the constituent materials of dentin, i.e., the peritubular dentin and the intertubular dentin matrix, and will relate the constituent properties to continuum behavior. The project establishes a model structure of dentin that is approximated by arrays of hollow ceramic cylinders imbedded in a ductile, mineral rich collagen matrix. The hardness and modulus of peritubular dentin and intertubular dentin will be measured using an atomic force microscope. The major hypotheses to be tested are that the properties of the peritubular dentin do not change with intratooth location and are isotropic, but those of the intertubular do change, are related to the mineral density of the intertubular matrix, and are anisotropic. Any age or gender-related differences in the properties will be investigated as well and related to changes in the constituents.